Assailants sprayed the car driven by Maksharip Aushev with bullets, killing him and wounding a passenger on a highway in Kabardino-Balkaria.

Aushev was a wealthy businessman known as an outspoken critic of Ingushetia's previous president, Murat Zyazikov, and the security forces operating in the region that he criticized for being corrupt and acting with impunity. He had been repeatedly threatened and was imprisoned for several months for disturbing public order.

Colleagues say that Aushev's killing is the latest in an effort to silence government critics and is particularly disheartening because of his good relations with Yevkurov and his efforts to draw attention to human rights abuses.

Aushev also still locked horns with Zyazikov's family, a powerful clan in the region, friend and activist Tanya Lokshina of Human Rights Watch in Moscow said.

Sadulayeva worked to rehabilitate children in war-torn Chechnya and was kidnapped and killed with her husband. After Estemirova was killed, her organization, Memorial, shut down its office and has yet to reopen.

Aushev's Murder Expected

Aushev was a successful marble merchant before he was forced into his recent activist role when his son and a nephew were arrested by security forces in 2007 and taken to Chechnya. Aushev used his power to buy information about their whereabouts and secure their release.

In the process, he organized large protests against the republic's regime, making himself an enemy of Zyazikov.

When journalist friend Magomed Yevloyev was killed by police in August 2008, Aushev took over his dissident Web site, continuing to rail against the authorities. A Yevkurov aide told Interfax Sunday that Aushev's murder was expected after Yevloyev was killed, and he feared they might not be the last.

"They've just been gone one by one, exterminated and every time such a killing happens, you wonder who's going to be next," Lokshina said. "The gaps between the killings have become so small."

Aushev survived a kidnapping attempt in September, after being pulled over by security forces in an armored vehicle. Lokshina said she believes they were federal security forces. He was coming back from a meeting with Yevkurov but managed to escape.

"All these people are different but, at the same time, they're being killed for demanding accountability," Lokshina said. "Until something is done about it, pretty soon there will be no one left. It's such a small group of people who dare to make these demands."